The present invention relates to a photomultiplier tube that converts weak incident light on a faceplate into electrons and performs detection using the electron multiplication effect created by dynodes that are stacked in multiple stages.
Japanese Patent-Application Publications Nos. HEI-6-314551 and HEI-6-310084 describe conventional photomultiplier tubes. The photomultiplier tubes include an electron multiplying section formed of dynodes that are stacked in multiple-layers and U-shaped connection terminals formed on the dynodes that connect the dynodes to stem pins. The connection terminals provided on each dynode are positioned such that lines passing through each connection terminal parallel to the dynode stacking direction do not overlap, in order to prevent electrical discharges from occurring between connection terminals. The dynodes are joined by welding together neighboring dynode plates. The positions of the welding seams are arranged not to overlap also.
Positioning the connection terminals and the welding seams in a manner described above is an effective method for increasing performance in the photomultiplier tube. In order to further improve the basic characteristics of the photomultiplier tube, however, it is necessary to also consider burrs that are generated when forming each dynode by an etching technique. The etching method for forming dynodes has been disclosed in Japanese Patent-Application Publications Nos. HEI-6-314552 and HEI-5-182631. However, this etching technique does not consider burrs that are generated during the process.
In view of the foregoing, it is an object of the present invention to provide a photomultiplier tube capable of suppressing noise generated due to burrs.
The photomultiplier tube of the present invention comprises a faceplate, a photocathode housed in a hermetically sealed vessel for emitting electrons in response to light incident on the faceplate, an electron multiplying section for multiplying the electrons emitted from the photocathode, and an anode for transmitting output signals based on the electrons multiplied by the electron multiplying section. The electron multiplying section includes a plurality of plate-shaped dynodes stacked in layers. Each dynode is formed with electron multiplying holes by etching and has an edge portion provided with bridge remainders. The bridge remainders are positioned such that-straight lines extending parallel to the stacking direction of the dynodes while through the bridge remainders on neighboring dynodes do not overlap each other.
In this type of photomultiplier tube, an etching technique is used to form electron multiplying holes in the plate-shaped dynodes that are stacked in multiple layers. To perform this etching process, a substrate surrounding a plate-shaped dynode and being connected to the same by a bridge portion is prepared. The dynode substrate is masked, and the etching process is performed to form a plurality of electron multiplying holes in the dynode substrate. Subsequently, the bridge portion is cut to form a dynode capable of being incorporated in the photomultiplier tube. Inevitably, part of the bridge portion remains on the edge of the dynode. It has been confirmed that when the dynodes are stacked with this bridge remainder, electrical discharge occurs between bridge remainders when the same are aligned in the stacking direction. This phenomenon becomes more marked as the interval between dynodes becomes smaller and has been confirmed through experiment by the inventors to generate noise in the photomultiplier tube. Therefore, the bridge remainders are arranged on neighboring dynodes in positions such that straight lines parallel to the dynode stacking direction and passing through each bridge remainder do not overlap, thereby further improving the basic characteristics of the photomultiplier tube. This technique is particularly effective when producing a thin type electron multiplying section. The present invention is predicated on the existence of burrs (bridge remainders) on the dynodes and recognizes that these burrs are an important element that cannot be ignored when trying to create a precision photomultiplier tube.
In the photomultiplier tube of the present invention, the bridge remainders are formed on edges along the edge portions of the dynodes. With this configuration, it is possible to form many arrangements of bridge remainders to suit various situations. For example, all bridge remainders can be positioned such that straight lines parallel to the dynode stacking direction and passing through each bridge remainder do not overlap.
In the photomultiplier tube of the present invention, the bridge remainders are formed on corners along the edge portions of the dynodes. With this construction, the bridge remainders can be arranged in the corners of every other dynode in the stacking direction.
In the photomultiplier tube of the present invention, the bridge remainders are positioned such that straight lines parallel to the stacking direction of the dynodes that pass through the bridge remainders overlap each other in every other dynode layer. With this construction, the bridge remainders can be separated by at least the thickness of a dynode.
In the photomultiplier tube of the present invention, all the bridge remainders are positioned such that straight lines parallel to the stacking direction of the dynodes that pass through the bridge remainders do not overlap each other. With this construction, the space between bridge remainders can be increased.
In the photomultiplier tube of the present invention, the bridge remainders are offset in a stair-shaped arrangement. With this construction, the space between bridge remainders can be increased more than the thickness of a dynode.